ICT 1 SINTEF Edge-On Sensor with Active Edge Fabricated by 3D-Technology T. E. Hansen 1), N. Ahmed 1), A. Ferber 2) 1) SINTEF MiNaLab 2) SINTEF Optical Measurement Systems

ICT 2 Background for this work is a SINTEF internal project: X-RAY IMAGING SYSTEM WITH PHOTON COUNTING AND BINNING Physical demonstration system to be realized before end of 2011 X-ray optics (collimators) Edge-on detector Substrate with detector and ASIC Backbone PCB Liquid cooling system Slightly curved to cope with X-ray point source

ICT 3 Guard ring width b g represents a dead region The edge-on silicon strip sensor configuration Incident radiation parallel to strips with total strip length serving as absorption length b a. p p Front contact Guard ring area Active area bgbg d Backside contact Incident photons baba P - diffusion N - substrate Parallel to strips With guard ring With active edge Guard ring on side facing incident photon replaced by N+ diffusion to stop depletion layer p p Front contact Rear side guard ring area Active area d Incident photons baba P - diffusion N - substrate N+ diffusion Backside contact

ICT 4 Edge-on X-ray sensor chip efficiency  Approximated efficiency: Q e = [1-exp(-  b a )] ∙ exp(-  b g ) Assumes total photon energy deposited in the sensor volume  Average number of generated electron/hole pairs N e per incident photon with energy E p (eV): N e = Q e ∙E p / 3.6 Advantages: 1. Higher efficiency than front illuminated sensors ≥ 20 keV 2. Potential use at ≥ 100 keV 3. Fast with response times in the10 to 20 ns region

ICT 5 Edge-on chip made at SINTEF MiNaLab Dimensions 25.7 x 12.9 x 0.5 mm 3 Example of edge-on silicon x-ray strip sensor with guard ring for material analysis application Guard ring area b g Active strips Incident photons Layout details: 256 strips, 50 µm width, 90 µm pitch 11.8 mm strip length

ICT 6 Scan from 31 to 164keV. Source 160keV tungsten tube X-ray test on edge-on sensor chip with guard ring Test restricted by sub-optimal front-end readout ASIC originally made to detect negative charge, not positive holes, and with insufficient dynamics)

ICT 7 Fabrication of edge-on sensor with active edge 6. Go on to planar processing 3. Oxidize edge 1µm 5. Back-etch polysilicon and planarize 1. DRIE etch 4µm trench 4µm 300µm oxide 2. Phosphorus diffusion (POCL) phosphorus 4. Deposit 1µm of poly-silicon poly-silicon

ICT 8 Edge-on x-ray sensor with active edge 64 sensor chips on 6-inch wafer Edge-on sensor chips with active edge fabricated at SINTEF MiNaLab 64 strips, width 80µm, length11.3mm, pitch 200µm Picture taken with chips on blue tape after sawing and expansion Part of side and rear guard ring Active strips Active edge Saw line Chip with 70µm distance strip –active edge Guard ring between strips Chip with 45µm distance strip –active edge No guard ring between strips

ICT 9 Edge-on x-ray sensor with active edge 64 sensor chips on 6-inch wafer SEM picture of active edge chip after dicing. Dicing not trivial, requires combination of DRIE etch and diamond saw Active edge Active strips Guard ring

ICT 10 between strips 64 chips per wafer: 50% of all chips with guard ring between strips 50% of all chips without guard ring between strips 8 reference chips with all guard ring 56 chips with active edge: 50% with 45µm distance strip to active edge 50% with 70µm distance strip to active edge

ICT 11 Edge-on x-ray sensor with active edge Measurements at wafer stage (6-inch wafer) Average breakdown voltage (BV) first tested wafer (56 chips on wafer with active edge) Distance strip to active edge45µm70µm Average BV190V 215V Depletion voltage (300µm)60V Total yield (BV > 120 V)85% Reference chip with guard ring on all sides Average BV: 340V

ICT 12 Edge-on x-ray sensor with active edge Measurements at wafer stage (6-inch wafer) IV-characteristics chip with 45 µm distance to active edge Strip leakage Guard leakage Depletion voltage compliance

ICT Test with 241 Am: 59.5 keV photons 13 Observed pulses Edge - On Silicon Sensor Mounted with much improved front-end readout ASIC

ICT 241 Am spectrum taken with edge-on, active-edge sensor non - cooled keV

ICT 241 Am spectrum taken with TE-cooled front illuminated Amptek Si PIN detector (6mm 2 ) keV

ICT Comparison with TE-cooled front illuminated Si PIN detector (6mm 2 ) 16 Active edge illuminated detector TE-cooled Si PIN-detector from Amptek

ICT 17 Comparison with TE-cooled front illuminated CdTe detector Active edge illuminated detector TE-cooled CdTe detector from Amptek

ICT 18 Conclusions and further work  Edge-on sensor chips with active edge has been successfully fabricated. Good breakdown, IV characteristics and yield  Edge-on sensor chips should cover the photon energy range ≤ 5keV to ≥ 100keV So far proved to 70keV  Almost comparable energy resolution with cooled CdTe detector at 59.5keV  We are in the process of procuring 57 Co sources for testing at 125 and 136keV. Expect results hopefully end of March. Will also use low energy sources to test efficiency of active edge

ICT 19 Thank you for your attention!

ICT 20 Measurements with low energy sources incident angle > 90 0 Angle of incident relative to edge > 90 0 to evade guard ring region. Isotope spectra ranging from Cu at 8.2 KeV to Ba at 32.2 KeV